Contouring strategies to improve the tensile properties and quality of EBM printed Inconel 625 parts

Xiaoyu Zhao,Amir Rashid,Sasan Dadbakhsh

doi:10.1016/j.jmapro.2020.12.007

Xiaoyu Zhao, Amir Rashid + Show 1 more

Open Access

https://doi.org/10.1016/j.jmapro.2020.12.007

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Abstract

Abstract This work systematically analyzes the influence of rough surfaces and porous subsurfaces in electron beam melting (EBM) printed components. Consequently, it applies various contouring strategies to improve the tensile properties of EBM printed Inconel 625 alloy parts. It is shown that no contouring (i.e., only hatching) creates a rough surface with numerous surface voids (as translated to surface notches). Although the commercially used multi-spot contouring can smoothen the surface to some extent (∼34 %), it fails to create a defect-free superficial region by leaving ∼25 % surface voids (translated to large surface notches) and ∼4 % subsurface porosity. These superficial defects form due to an interrupted shrinkage, occurring on the surface and in the contouring region. In contrast, optimal post-hatching high energy continuous contouring creates a thick and consistent post-hatching track that can successfully reconsolidate surface voids remaining from the hatching step. In comparison with the multi-spot contouring, this reduces the surface and subsurface porosity down to ∼10 % and ∼0.4 %, respectively, and hence increases the apparent stiffness by ∼140 %, tensile strength by ∼105 % and elongation by ∼260 %. This nearly reaches the mechanical properties of the conventionally machined parts (UTS ∼635 ± 20 MPa and elongation ∼50 ± 2 %).

Highlights

Electron beam melting (EBM) is a metal additive manufacturing (AM) process to fabricate near-net shaped parts by selectively fusing a powder bed using an electron beam
EBM contouring defects appeared at two levels: i) surface and ii) subsurface, which deteriorated the quality and performance of the parts
The commercially used multi-spot contouring strategy created a track with an inconsistent width, a bumpy surface, and many voids at neighboring spots

Summary

Introduction

Electron beam melting (EBM) is a metal additive manufacturing (AM) process to fabricate near-net shaped parts (commonly for medical devices and aerospace components) by selectively fusing a powder bed using an electron beam. The energy source in EBM is high-speed elec trons, the electron beam – material interaction can pose many challenges. The first issue is ‘smoking’, which originates from the elec trostatic charges blowing away the powder particles. To prevent smoking, preheating to a high temperature is compulsory to sinter the powders, mitigating the static charges and powder jumping [1]. This process has a unique working condition, being at a high temperature under vacuum. EBM is highly susceptible to the formation of material defects such as internal pores and cracks [2]

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